1. Field of the Invention
The present invention relates to a toner for use in recording methods that employ, for example, electrophotography, electrostatic recording, toner jet recording, and so forth. More particularly, the present invention relates to a toner for use in copiers, printers, and facsimile devices that produce a fixed image by forming a toner image on an electrostatic latent image bearing member, subsequently forming a toner image by transfer to a transfer material, and fixing this toner image by the application of heat and pressure.
2. Description of the Related Art
Achieving a lower energy consumption has in recent years been regarded as a major technical issue also for electrophotographic devices, and an example in this regard is obtaining a substantial reduction in the amount of heat used by the fixing apparatus. Accordingly, with respect to the toner, there is increasing need for fixing to be made possible at lower temperatures, that is, there is increasing need for “low-temperature fixability”.
Endowing the binder resin with a sharper melting behavior is already known as an effective method for enabling fixing to occur at lower temperatures. Polyester resins exhibit excellent properties in this regard.
Viewed from another perspective, i.e., that of raising the image quality, reducing the toner particle diameter and providing a sharper toner particle size distribution are pursued in order to increase the resolution and definition, while a spherical toner is suitably used for the purpose of improving the transfer efficiency and flowability. Wet methods have entered into use as methods for efficiently producing spherical toner particles that have small particle diameters.
The “solution suspension” method has been introduced as a wet method that can use sharp-melting polyester resin (Patent Reference 1). In this “solution suspension” method, spherical toner particles are produced by dissolving the resin component in a water-immiscible organic solvent and dispersing this solution in an aqueous phase to form oil droplets. This method can conveniently provide a spherical toner that has a small particle diameter and that employs a binder resin of polyester with its excellent low-temperature fixability.
Within the sphere of the aforementioned toner particles produced by the solution suspension method and having polyester as the binder resin, capsule-type toner particles have also been introduced with the goal of an even lower low-temperature fixability.
The following method is provided in Patent Reference 2: polyester resin, an isocyanate group-functional low molecular weight compound, and other components are dissolved and dispersed in ethyl acetate to produce an oil phase and liquid droplets in water are produced. As a result, the interfacial polymerization of the isocyanate group-functional compound at the liquid droplet interface yields a capsule toner particle having polyurethane or polyurea for its outermost shell.
Patent References 3 and 4 each provide a method in which a toner base particle is produced by the solution suspension method in the presence of resin microparticles of at least one selection from vinyl resins, polyurethane resins, epoxy resins, and polyester resins and in which a toner particle is produced in which the surface of the toner base particle is coated by these resin microparticles.
Patent Reference 5 provides a toner particle obtained by a solution suspension method that employs urethane-modified polyester resin microparticles as a dispersant.
Patent Reference 6 provides a core/shell-type toner particle composed of a shell layer (P) of one or more film-like layers comprising polyurethane resin (a) and one core layer (O) comprising a resin (b).
This core/shell-type toner particle has a configuration in which the core portion is caused to have a low viscosity and the deterioration in the resistance to hot storage is compensated by the resistance to hot storage of the shell portion. In this case, a strategy is required in order to provide a shell portion that is somewhat robust to heating, e.g., strong crosslinking or a high molecular weight, which results in a tendency for the low-temperature fixability to be impaired.
When, in particular, a urethane resin is used as the dispersant, the resistance to hot storage declines in accordance with the decline in the softening point of this resin. It therefore becomes necessary to provide a urethane resin that satisfies the desired Tg and that is sharper melting. However, when the desired urethane resin is obtained by carrying out a urethane formation reaction using a plurality of monomer species, for example, monomer with a functional group moiety that provides resistance to solubility in solvent, monomer for adjusting the softening point, and so forth, the difference in reaction rates causes a broadening of the molecular weight, which as a result impairs the ability to achieve a sharp-melt property for the toner. In addition, when these functional groups are decreased, the particle size distribution becomes nonuniform and/or the resin becomes buried in the toner particle and the ability to form a shell layer is impaired.
Moreover, when a shell layer is formed at the toner particle surface using a urethane resin as the dispersant, the functional group characteristics tend to be picked up by the toner's charging behavior. As a result, problems tend to appear with the charging behavior and stability under various environments.
Due to this, the development is required, from the perspective of both toner production and toner properties, of a dispersant that employs an improved urethane resin.
Patent Reference 1: Japanese Patent Application Laid-open No. H08-248680
Patent Reference 2: Japanese Patent Application Laid-open No. H05-297622
Patent Reference 3: Japanese Patent Application Laid-open No. 2004-226572
Patent Reference 4: Japanese Patent Application Laid-open No. 2004-271919
Patent Reference 5: Japanese Patent No. 3,455,523
Patent Reference 6: International Publication WO 2005/073287